Frequency converter



Oct. 1, 1946. J. w. CLARK FREQUENCY CONVERTER Filed Julie 19, 1941 2Sheets-Sheet 1 NV N J W CLARK d- 1, 1946- J. w, CLARK 2,408,410

' I FREQUENCY CONVERTER v Filed June 19, 1941 2 Sheets-Sheet- 2 PatentedOct. 1, 1946 FREQUENCY oo vvitarr'za JohnW. Clark,'Chatham, N: J.,assiaom Beu- .Telephone Laboratories, Incorporated, New ,York, vY acorporation Qf INCWJYOIK This invention relatesto modulating system forultra-high frequency electromagnetic waves and currents and isparticularly applicable towaves a few centimeters or less inwave-length.The invention relates more especially to afrequency converter, mixer, orfirst detector in a superhetero dyne'radio receiving system.

An object of the invention is construction and operation of 'asuperheterodyne radio receiver adapted for usein the ultra-lushfrequency a l I A feature of the-inventionis .a compact means forintroducing a received sign'al wave into the interior of a hollowresonator in an ultra-high frequency electron velocity variation type ofoscillator to effect frequency conversion with no substantialdisturban-ce tov the normal operation of the oscillator and with highefliciency of conversion.

Another feature. of the invention resides in impressing the receivedsignal-modulated wave between the drift tube and the adjacent elec-:trodes in a'single cavity type of oscillator, ef-

fectively across. the. input .andoutput gaps, in

parallel. I

1 lnaccordance with the invention, the beating oscillator is of atype-employing electron velocity variations, operated substantially inthe normal manner, and provision is made for impressing the incomingsignal modulated wave substantially simultaneously across the input andoutput gaps efiectively in parallel. A velocity variation inaccordance'with the'incorning wave is superposed uponthe velocityvariation due to The velocity varied electhe local oscillations. tronstreamisthen subjected to a conversion process to develop densityvariations. Anynon linearity in the conversion process will result inthejappearance of modulation components, for

example, sum and difference frequencies, in the density variations. To'secure'airelatively low intermediate frequency, the differencefrequency component maybe utilized. vThe modulation componentsmay bedeveloped; at the collector electrode in various ways, as, forexample,by

operating the collector at a-retarding' potential adjustedto turnbackthe slower moving electrons; Alternately, the collector electrodemay be operated at an electron'accelerating 'potential'or asubstantially field-freedrift space may be proto simplify thepartiallycut away;

Application June 19, 1941, Serial No; 398,757

1 Claims. (01.31545) 7 modified inaccordance' with the' invention, shownFigs.- 1A} and 1B show-alternativedetails which may be substituted inthe'arrangement of Fig. 1 'Fig.'2' is an end viewof the structure ofFig. 1, shown partially cut away; I

' of a superhetero- Fig. 3 is a schematic-diagram dyne-radio receiverembodying the invention; "and vided .inwhich bunching' ofithe :electronsmay 7 take place in any suitable manner. :Inthe drawings: l 1

Fig. 1 is aperspective .viewiof" an oscillator- Fig. 3A showsanalternative coupling arrangement which maybe substituted for a portionof the circuit showninFigJi. I

Referring to the drawings, there is shown in Figs. 1 and 2 a resonantcavity oscillator of the electron velocity variation type such as isdisclosed in application Serial No. 386,794 filed April 4,1941, by A. E.Anderson andA. L. Samuel and assigned to the assignee ofthe presentapplication. My oscillator structure herein disclosed includes certainmodifications to accommodate the introduction of waves intercepted by adoublet antenna l, or other-ineans'of intercepting ultrahigh frequencypo'wen The respective branches of the antenna'or other interceptorareconnected with the outer conductor 2 and inner con ductor 3 of asuitable coaxial transmission line, The line 2, '3 preferably has twobranches, one'of which; compris'ingan outer conductor 4 and aninnerconductor 5, is an adjustable tuning stub.

The other branch, comprising "an outer conductor 6 and 'an innerconductor "lfis fitted through an in the semicylindrical casing section2| aperture of the Anderson-Samuel oscillator. Throughout thedrawings-the elements which are the same as corresponding elements inthe Anderson-Samuel oscillator have been given'the same referencenumeralas in the drawings of the Anderson-Samuela'pplicationfl Thecylindrical insulating envelope lll'oftheoscillator, for example, aglass tube, encloses 'an electron gun shown generally at llg'togethe'rwith an electron collecting electrode or collector 'IZ. Betweentheelectrongun II and the collector lz'there are sealed into and throughthe walls ofthe envelope In a pair of disc members'fj3 and M formedrespectively into protruding, approximately conical" electrodes l5 andI6, coaxial with'the electron gunand provided with alignedapertures attheir respective apices for'the passage-therethrough of an electronstream 'or beam from the electron gun. A

tube l1, referred to herein'as the drift tube, is axially mountedbetween the electrodes l5 and I6 and has aligned apertures at its endsfor themtrance and exit of the electron beam. The'electrodes l5 and I6,in cooperation with the respec-- tive adjacent ends of the disc 'tubel'l, form a pair it of gaps l8 and I9 spectively as the input gap andthe output gap. The discs l3 and I4 and the drift tube I! are preferablyof highly conductive material, for example, copper. The discs l3 and Mare hermetically sealed into and through the walls of the tube by anysuitable process or form of seal, for example, a copper-glass seal. Thedrift tube H has attached to it a conductive rod 20, by which it issupported in position and by means of which electrical contact may bemade from the exterior of the envelope Ill. The conductor 20 is sealedinto and through the Wall of the envelope l0 through a glass bead orother. suitable hermetic seal. Alternatively, three supporting rods H,12 and 13 may be employed as shown i'n' Fig.

1A, or the drift tube may be supported by-a disc 1 electrode 14 as shownin Fig. 1B. The inner conductor is conductively connected to the drifttube I! in any suitable manner as, for example, by means of the rod20,0rby one of the rods 1|, 12 and 73 shown in Fig. 1A, orby=connectionto the-disc electrode 14 of Fig. 1B. The outer conductor 6is conductively connected to-the casing 2| as by means of a snugfrictional engagement or in other suitable manner. 4 The tuning stubcomprising the outer conductor 4'and inner conductor 5 may beadjustedby-means of an annular piston 8 of conductive material connected by rodsor other suitable means with a knob 9. 7

Inthe oscillator, the ,discs |3- and |4 form a portion ofthe walls ofthe resonant chamber or cavity resonator together with thecasing"sections ZI and 22, which sections'fit closely together and are providedwith milled semiannular surfaces 23'and 24,respectively, which fitssnugly inside the edges of the disc members |-3 and M. A pairofcylindrical collars 25 and '26 of magnetic material, provided withflanges Z'Iand 28, respectively, are placed over the tube 10- andagainst the outer surfaces of the respective disc members |3and M. 0mone-side of the casin'ga ring 6| and-screws are provided so that whenthe screws are tightenedithe disc -3-and flange 21 are clamped securelybetween thering BI and surfaces 23 and 24 on the casing. A

similar ring, 62 and screws 29 areprovided on theotherside of thecasing.

v, A plurality of plungers, in the formof-screws 3 4, 35, 36 and 31, arethreaded into the walls of thecasin'g sections 2| and 22 for alteringthe size and shape of the resonant cavityfor tuning purposes.

A permanent magnet 45 has pole-pieces' extending perpendicular to themain body the pole-pieces being milled out with cylindrical-depressionsat 46 and '41 to form a cradle to support the cylindrical collars and26, respectively. The tube assemblyincl-uding the collars is held to thepermanent magnet by the magneticforce and, in addition, the lower halfsection 22 of the casing-may be securedto the middle portion of-thepermanent magnet by means of a screw;48. If desired, the magnet may beattached to a base plate or other mounting in any suitable manner. .AU-shaped magnet or one of other, suitable shape may be used inplaceof-the one illustrated, or an electromagn'et may be substituted forthe permanent'magnet.

The electron gun may be of thetype dis closed in Figs. 3 and 4 of theAnderson-Samuel application, comprising adished cathode 49erranged to beheated'by a heating element, 50-,as shown schematically in Fig. 3herein. A shape which will be referred to re-- mg electrode 5| forforming the electrons emitted from the cathode 49 into a conical beam incooperation with the shape of the cathode may be provided in thevicinity of the cathode as shown schematically in the figure. Theelectrode 5| is preferably electrically connected with the cathode. Anaccelerating electrode 52 serves to regulate the beam current and inconjunction with the shaping electrode 5| to focus the beam atapproximately the center of the input gap l8. One side of the heatingelement 50 may be connected to the cathode Within the tube ID andbrought out of the tube by means of the common lead 53. In that case,the lead 53, together Withithe remaining'heater lead 54 and a lead 55from the accelerating electrode 52 constitute the external connectionsfrom the electron gun. The'remaining electrical connections to theoscillator comprise a lead 56 connected with the walls of the resonantchamber, which lead 55 may conveniently be grounded or connected withthe mounting .plate, and a leadfilconnected to the collector l2. Theleads 53, 54, 55' and .51 are brought out through the walls of the tubeIll-in suitable presses or scale.

The interconnections of the tube with suitable sources of biasingpotential andheating-current are shown schematically inFig. 3. 58 isapower transformer or other source of suitable current for operating theheating element 50. The lead 53 is connected to the negative terminal ofa biasing battery or other source of biasing potential '59. The lead 55from the accelerating electrode 52 is connecte di't'o the variablecontactor of a potentiometer 50,, one ofthe two potentiom'eters '60 and'Iil connected in shunt across the battery 59. The lead '55 from theresonator is connected to the variable contaotor of the potentiometer l0and maybe grounded. Ifdesired, the potentiometers 60 and 10 may bereplaced by asing'le potentiometer "with two contacts, either orboth'c'f which contacts may in some cases befixed.

The head" 51 from-the collector 12" is connected to the common terminalof'a resistor and a condenser 8|, the remaining terminal of'thecondenser being connected 'to "one of the input terminals of anintermediatefrequency amplifier 82'. The remaining input terminal of theampli fier 8-2 is preferably grounded. The remaining terminal of theresistor is connected-"to a point in the power "supply circuit,forexainp le;

eitlier'to the negative or to-th-e pos-itive terminal of the battery 59.A switch 851s shown inFig. 3 whereby either of 'the latter-two"connections may be selected as desired. The I output tennin'als of theintermediate freqlie'ncy amplifier 82 are connected to the'inputterminals of a detector "84:, whi'chis :connecte'dwto asuitable-translating device such as a 'telephone receiver =85.

alternative coupling --arrangement for use between the collector I2 :andthe intermediate frequency. amplifier :821 is shown 1 Fig. 3 3A and maybe substituted for "thezportioniof the circuit in Fig. 3: shown between:the broken .li'n'e's .X' and Y. In Fi'g.i3A,:86 is a transforr'nersuitablefor' 'pedance ratio 'tomatch the impedance or the Vcollector-circuit,.which maybeof'the order of fillflfliohms'rx.11; I Q f3'.-In the operation of the system as shown in the figures; Etheoscillator functions to sustain electrdmagnetic waves of ultra-highfrequency. with-. in the resonant cavity .in substantially. the same vintensity inthecavity, and, therefore,:do not ma-y terially alter theconfiguration of the field.*The main differenceis asmall changeintheeffective shape'and-volume of the cavity and a resultant difference-ginnthe resonating;frequency, ,1 which maybe allowed for inithetdesignxof .the. resonator. The :function of .the =.oscillator;in thepresent arrangementi's-to establish a'strong electric field of the.:resonant frequency across both, the input gapE'. l.8t-and.,theoutputgapilll. The antenna l is.-idesigr'ied for the reception ofadesired high frequency and; theresonant frequency of the oscillator ispreferably chosen to differ from the frequency to be'received upon theantenna by an amount, fjust equal to -a desired intermediatefrequency.:.-,'Ih'e piston 8 is adjusted to resonate therline;totheincoming frequency in known mannento impress,a;maxi1num alternatingvoltage upon .thedrift: tube IL The voltage, thus ape plied iseffectively in parallel between the drift tubeand the electrodes: I3 andI4, respectively.

Referring more specifically to the operation .01

the syste'm .as' afmodulator, frequency converter or first detector, itwill be evident that the incoming signal waves and the locally generatedwaves are superimposed upon the input gap [8 and the output gap IS insuch manner as to simultaneously impressvelocity variations upon theelectrons passing through the gaps. known that velocity variations in anelectron stream may be converted by various means into successions ofdensity variations of the same effectediby a sorting out of theelectrons on the basis of theirxvelocity, the f aster electrons enter-'ing the; collector. .The process is analogous to rectification and inaisimilar manner, as in the useof a'rectifier' as a modulator orconverter; sumland difference frequencies are produced in the resultantcurrent. The difference frequency with re'spectto the incomingwaves.andthe local oscillations'is usually chosen as the intermediatefrequency in order to take advantage of a relatively 1 low frequency inthe intermediate frequency. amplifier. The modulation products in thecollector circuitcarry theoriginal signal modulationi-asfrec'eivedatthe'antenna and the intermediate freq'uency compone'ntlmay be selected,and, amplified-,4 and-ksubjecteduto .a second detection toreproducestheoriginal signals as in any superheterodyne radio receiving system. Theintermediate frequency amplifier82, detector 84 anditranslating'device85 are not shown in detail, asthey-maybe of any suitable type... f Whentheswitch 83 is placed in the upper position,;the.collector isconnectedto a positive portionxof source 59, or other suitable potential toprovide an.-.electron accelerating effect .in the spacebetween'theoutput gap [9 and the collector 1 2.. ..Allthe. electrons, in this case,are drawn to the collector :but due to their unequal velocities they.become, somewhat grouped into. bunches while .traversingithe distancebetween the output gap1l9 and thecollectorJZ. Itis. known that thisprocess of .bunching is generally a non-linear one... Consequently,modulation components appear. in the density variationsof the; electronstream: asfiit .-'strikes .the .collectorelectrode; l2, and, an;intermediatev frequency component, is im-v pressed upon the couplingcircuit with results similar to those describedin the preceding case.

. What-is claimed is:

stream at some point later traversed by the stream. It is also knownthat the process of conversion from velocity variations to densityvariations may be a non-linear one, so that modulation products such assum and difference frequencies appear in the density variations soproduced. In the present system, the conversion may be accomplished inat least two ways, either one of which may be selected by means of theswitch 83. In accordance with one method, the switch 83 is placed in thelower position, as shown, so as to connect the collector I2 to thenegative terminal of the battery 59, thereby placing the collector atsubstantially the same direct current potential as the cathode 49. Theelectrons, after passing the output gap I9, are in this case subjectedto a strong retarding field. Having different velocities, the individualelectrons possess different amounts of kinetic energy and are able topenetrate respectively different distances against the retarding fieldbefore being stopped and their motion reversed by the field. By properadjustment of the initial velocity of the electron stream, it ispossible to arrange matters so that the faster electrons strike thecollector l2 while the slower electrons are turned back. The densityvariations above referred to are in this case 1. In a frequencyconverter, an oscillator comprising a resonating chamber for ultra-highfrequency waves, a drift tube enclosed within said chamber, and saidchamber walls and. said drift tube having aligned apertures, means fordirecting a stream of electrons through said apertures whereby saidelectron stream is velocity varied by electromagnetic waves within saidchamber, and means for adjusting the transit time of the electronstraversing said drift tube to initiate and sustain said oscillations;means for impressing between said drift tube and said chamber walls aWave having a frequency comparable to but different from the frequencyof said oscillations whereby a second velocity variation is superposedupon said electron stream, and means non-linearly responsive to velocityvariations of said electron stream, operative upon a doublyvelocity-varied portion of the stream.

2. A system in accordance with claim 1 in which the non-linearlyresponsive means comprises means for sorting electrons on a basis ofdifferent electron velocities.

3. A system in accordance with claim 1 in which the non-linearlyresponsive means comprises mean for converting velocity variations ofthe electron stream into electron density variations in the stream.

4. A system in accordance with claim 1 in which the non-linearlyresponsive means comprises means for grouping electrons into bunches inaccordance with their differing velocities.

5. In a frequency converter, an oscillator comprising a resonatingchamber for ultra-high frequency waves, a drift tube enclosed withinsaid chamber, and said chamber walls and said drift tube. havingaligned. apertures, means for direct-, inga .streamof electronsthrough'said "apertures whereby said electron stream is velocity variedby.electromagnetic oscillations Within said chamber, and means foradjusting the transittimeof the electrons traversing said drift tube toinitiate and sustain said oscillationsya coaxial line for ultra-highfrequency waves, said line extending radially through the Wall of saidchamber, the outer conductor of said line being conductively connectedto the walls of said'chamber and the inner-conductor of said line beingconductively connected "to said drift tube, means for impressing uponsaid coaxial line waves having a vfrequency comparable to butdifferent.from the frequency of said oscillations'and non-linearly operativemeans responsive'to velocity. variations of said electron stream.

6. In a frequencyconverter, :aresonating chamber for ultra-highfrequencywaves, the wall of said chamber being apertured to admit .anelectronstream into the interior'thereof, means to inject an electronstream through saidaperture, a drift tube supportedwithin saidresonating chamber, said drift tubecbeing arranged to surround saidelectron stream and to define together with the chamber Wall a pair ofgapstraversed by saidielectron stream, means cooperating .with saiddrift tube, said chamber wall, and'said electron stream for producingsustained electromagnetic oscillations within said resonating chamberat. a resonant frequency thereof, r a transmission line havingconcentric inner and outer .conduc tors extending in a directionperpendicularto the linesof force of the electric field within said.res-. onating chamber, said-transmission line-passing through the wallof said resonating chamber-and extending through a substantial portionof the interior space of said resonating chamber, means electricallyconnecting the outer conductor. of said line to thewall of :saidvresonating chamber, means electrically connecting the innersconduc'torof 1 said line .to said= drift tube "and an external wavesourcewconnected to said'transmission line.

'7. In a frequency converter, .a resonating chamber forultra highfrequencywaves,.the';wal1 of said chamber being apertured to admitanelectron stream into the-'rinteriorythereof, means'to injectanelectron streamuthrough saidaperture, a drift tube supportedwithin:said1 resonating chamber, said drift tube being arranged 1 tosunround said electron stream and to define together with the chamberwall a. pair of gaps traversed by. said e1ectron-stream,x meanscooperating with said drift tube; said chamber walLandzsaid electronstream to produc .sustainedelectromagnetic oscillations withinsaidresonating chamber at aresonant 'frequencythereof,aitransmissionzlin'e having 'concentricinner-andi outer. conductorsv ex.tending in av direction substantially perpendicular to the linesof'forceof' the electric fieldwithin said resonating chamber, saidtransmission line passing through "the wallof said resonating chamberand extending through a substantial portion of the interior space ofsaid resonating chamber, means electrically.connecting the outerconductor of saidlinetozthe wall of .said'resonating chamber, meanselectrically connecting the innerwconductor of said lineto said drifttube, an externalwave source connected-to saiditransmission line andmeans for tuning said transmission line to the frequency :of.saidexternal wave source to impress substantial .poten'tialsatthefrequency of said.externaliwave'source across. at leastone of said gapsinsuperposition.withpotentials developed by said sustainedelectromagneti oscillations.

:JOHN W. CLARK.

